1. Field of the Invention
The present invention relates to a fuel injector.
2. Description of the Related Art
A fuel injector which is opened by moving a needle with the aid of a fuel pressure in a high pressure passageway, wherein a pressure chamber defined by the rear surface of the needle and connected to the high pressure passageway is formed in the fuel injector and a restricted opening and a check valve are arranged such that fuel easily flows in the region between the pressure chamber and the high pressure passageway but the flow out of fuel from the pressure chamber is restricted to thus raise the fuel injection pressure and maintain a good fuel injection completion is known (see Japanese Unexamined Utility Model Publication No. 1-114979).
When a large quantity of fuel is supplied into each combustion chamber of a diesel engine, to be burnt therein, the fuel is quickly burnt upon the ignition thereof. Accordingly, the combustion pressure is quickly raised, and this results in a generation of noise. To prevent a sudden rise of the combustion pressure when the fuel is ignited, the ignition should occur when only a small quantity of fuel exists in each combustion chamber, the quantity of fuel to be supplied into the combustion chamber gradually increased thereafter, and the increased quantity of fuel successively burnt to thereby gradually raise the combustion pressure. Therefore, preferably a fuel injection rate of fuel from the fuel injector is gradually increased. Namely, the fuel injection rate is gradually increased with an elapse of time from the time at which the fuel injection is started. Further, when the engine operates at a high engine speed with a large torque at an engine shaft, preferably the fuel injection rate is quickly raised because a large quantity of fuel must be supplied to each combustion chamber a short time. Namely, preferably the raising of the fuel injection rate is varied in accordance with the current running state of the engine.
With the conventional fuel injector as described above, however, since a pattern representing the fuel injection rate is based on a diameter of the restricted opening, a problem arises in that the fuel injection rate pattern cannot be varied to a desired fuel injection rate pattern corresponding to the current running state of the engine.